We studied the phenology and reproductive biology of the stained glass palm Geonoma epetiolata in a premontane rain forest of Costa Rica. This understory species is endemic to Costa Rica and Panama. We followed 102 plants for two years and found that G. epetiolata is monoecious and protandrous. Flowering duration at the inflorescence level is three to six months for the male phase and two to three weeks for the female phase; this is one the most extended flowering periods reported for palms. Flowering in this palm is continuous throughout the year, both at the individual and population level. This long and continuous flowering pattern may represent an adaptation to increase the chances of reproduction in a environment of high and unpredictable rainfall. The species is self-compatible, but self-pollination is possible only when there is overlap of male and female inflorescences (38% of the cases). Only 28 percent of the stigmas of 1020 flowers received pollen grains and 20 percent developed pollen tubes in the styles. Of all the flowers produced by an inflorescence, 14 percent initiated fruit development but only 3 percent develop into mature fruits. Seventy-six percent of the initiated fruits were aborted.